The mechanisms behind aging and longevity are a current topic of investigation. Much progress has been made studying the genetics of cellular aging in yeast. Yeast cell divisions produce a detectable remnant on the cell wall of the mother cell, known as a bud scar. Cellular aging in yeast is related to the number of daughter cell progeny a cell has produced. By counting the number of bud scars on the mother cell wall, the number of divisions, and thus the age of the cell, can be determined. A similar marker of previous cell divisions would be useful for studies of cellular aging in mammals.